Glass fibers are often protected from external forces with one or more coating layers. Typically, two or more layers of coatings are applied during the optical-fiber drawing process (i.e., whereby a glass fiber is drawn from an optical preform in a drawing tower). A softer inner coating layer typically helps to protect the glass fiber from microbending. A harder outer coating layer typically is used to provide additional protection and to facilitate handling of the glass fiber. The coating layers may be cured, for example, using heat or ultraviolet (UV) light.
UV curing requires that the coated glass fiber be exposed to high intensity UV radiation. Curing time can be reduced by exposing the coating to higher intensity UV radiation. Reducing curing time is particularly desirable to permit an increase in fiber drawing line speeds and thus optical-fiber production rates.
Mercury lamps (e.g., high-pressure mercury lamps or mercury xenon lamps) are commonly used to generate the UV radiation needed for UV curing. One downside of using mercury lamps is that mercury lamps require a significant amount of power to generate sufficiently intense UV radiation. For example, UV lamps used to cure a single coated fiber (i.e., one polymeric coating) may require a collective power consumption of 50 kilowatts.
Another shortcoming of mercury lamps is that much of the energy used for powering mercury lamps is emitted not as UV radiation but rather as heat. Accordingly, mercury lamps must be cooled (e.g., using a heat exchanger) to prevent overheating. In addition, the undesirable heat generated by the mercury lamps may slow the rate at which the optical-fiber coatings cure.
Furthermore, mercury lamps generate a wide spectrum of electromagnetic radiation, such as electromagnetic radiation having wavelengths of less than 200 nanometers and greater than 700 nanometers (i.e., infrared light). Typically, UV radiation having wavelengths of between about 300 nanometers and 400 nanometers is useful for curing UV coatings. Thus, much of the electromagnetic radiation generated by mercury bulbs is wasted (e.g., 90 percent or more). Additionally, glass fibers typically possess a diameter of about 125 microns or less, which, of course, is much smaller than the mercury bulbs. Consequently, most of the UV radiation emitted by the mercury lamps does not reach the glass fiber's uncured coating (i.e., the energy is wasted).
It may thus be advantageous to employ UVLEDs to cure glass-fiber coatings as an alternative to conventional mercury lamps. UVLEDs typically require significantly less energy and correspondingly generate much less heat energy than conventional UV lamps.
By way of example, U.S. Pat. No. 7,022,382 (Khudyakov et al.), which is hereby incorporated by reference in its entirety, discloses the use of UV lasers (e.g., continuous or pulsed lasers) for curing optical-fiber coatings. U.S. Patent Application Publication No. 2003/0026919 (Kojima et al.), which is hereby incorporated by reference in its entirety, discloses the use of ultraviolet light emitting diodes (UVLEDs) for curing optical-fiber coatings.
Although efficiency is an important consideration in selecting a curing apparatus, it is also desirable to employ a curing apparatus that is capable of curing optical fibers quickly. In particular, it is desirable to employ a curing apparatus that is capable of curing optical fibers that are moving at commercial draw speeds.
Therefore, a need exists for a curing apparatus that is capable of operating at commercial draw speeds and, as compared with a conventional curing apparatus employing mercury lamps, operates with improved efficiency.